Pulsed plasma accelerator and method

ABSTRACT

A pulsed plasma accelerator includes two electrodes ( 1 ) arranged between dielectric bars ( 2 ) made from an ablating material, a discharge channel with an open end part whose walls are defined by the surfaces of electrodes ( 1 ) and dielectric bars ( 2 ), an energy accumulator ( 11 ) and current supplies ( 14,15 ) for connecting the electrodes ( 1 ) with the energy accumulator ( 11 ). The current supplies ( 14, 15 ) define in conjunction with the electrodes ( 1 ) and the energy accumulator ( 11 ) an external electric circuit, with characteristics of the external electric circuit being selected on the condition: 2≦C/L, where C(μF) is the electric capacitance of the external electric circuit, and L is the inductance of the external electric circuit, L≦100 nH. During operation of the plasma accelerator, quazi-nonperiodic pulse discharges are ignited and maintained in the discharge channel. By providing coordinated parameters of the external and internal circuits, a substantial increase in the efficiency of plasma acceleration is achieved.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase of International Application SerialNo. PCT/RU2004/000368, filed 20 Sep. 2004.

BACKGROUND OF THE INVENTION

1. The Field of Invention

The invention relates to plasma equipment and plasma processes, inparticular, to plasma accelerators and plasma acceleration methods,which may be primarily employed for creating of a propulsive force, forexample, a space-borne electric propulsion, as well as for generating ofhigh-speed plasma flows in experimental investigations and model tests.The invention may be also employed for realizing various processes fortreatment of products and modification of material properties.

BACKGROUND OF THE INVENTION

It is customary to assume that plasma accelerators are apparatusesdesigned for ionization of a working substance accompanied byacceleration of an ionized gas (plasma) under the action ofelectromagnetic force and gas pressure force upon generation of anelectric discharge.

Plasma acceleration occurs in plasma accelerators as a result of anelectric breakdown in an electrode-to-electrode gap. In steady-stateplasma accelerators, the electric discharge time is sufficientlylong—the typical breakdown time t is at least 1 second. In pulsed plasmaaccelerators, the electric discharge is of shorter duration. The pulseddischarge time t is about 1-100 μs.

Pulsed plasma accelerators are currently employed as actuating systemsin spacecraft control systems and as pulsed low-temperature plasmainjectors.

It is common knowledge that in order to maintain a spacecraft in adesired orbital position during retarding in a relatively dense residualatmosphere of the outer space, it is advantageous to use small-sizedpropulsion units with low power consumption. Such requirements aresatisfied with the use of propulsion units based on pulsed plasmaaccelerators. Most of such propulsion units use solid dielectric as aworking substance releasing gaseous products as a result of ablationunder the action of thermal and radiant energy of an electric dischargegenerated.

There is a great tendency nowadays to a wide employment in the outerspace of low-orbiting (with orbit height Horb=400-1000 km) light-weightand small-sized spacecrafts of relatively simplified construction andlow cost, said spacecrafts having the typical weight in the range offrom 50 kg to 500 kg. However, these light-weight and small-sizedspacecrafts have substantially restricted power supplying capacities ofelectric propulsions providing high accuracy in keeping of orbitalparameters of both individual spacecrafts and groups of suchspacecrafts. For this purpose, highly efficient small-sized electricpropulsions capable of correcting and stabilizing of spacecraft orbitsat the minimal power consumption are demanded.

Steady-state plasma accelerators used as spacecraft controlling electricpropulsions have a number of grave disadvantages including thecomplexity of plasma accelerator construction, the complexity of amanufacture process and operation of an accelerator, the increasedmanufacture and operating costs, as well as insufficient propulsiveefficiency (plasma acceleration efficiency) and low performancereliability at the power consumption of less than 150 W.

An ablation pulsed plasma accelerator is the most promising propulsionfor a spacecraft with regard to the simplicity of construction,reliability, low costs and proper functioning at the power consumptionof from several watts to hundreds of watts. A pulsed plasma acceleratoralso provides for maximal accuracy of spacecraft control as compared toother kinds of propulsion units used as actuating systems. However, theefficiency of pulsed plasma accelerators of the prior art does not meetthe operative requirements for handling the majority of spacecraftcontrol problems.

A substantial increase in the operating efficiency of a pulsed plasmaaccelerator, primarily over the range of power consumption of from 20 Wto 300 W, within which the basic problems for controlling of spacecraftorbital parameters are currently solved and will be solved in the nearfuture, is of fundamental importance for widening the range offunctioning of a spacecraft.

Presently the basic technical problems of a pulsed plasma acceleratorare the excessive retardation of evaporation of a working substance withregard to a discharge current and, as a result, ineffective accelerationof a substantial part of plasma generated, which on the whole adverselyaffects the efficiency of accelerator (the efficiency of plasmaacceleration).

It has already been pointed out in the very first studies on theinvestigation of plasma acceleration processes in a pulsed plasmaaccelerator (Artsymovitch L. A. et al, “Electrodynamic acceleration ofplasma coagulates”. ZHETF, Moscow, 1957, vol 33, No. 1) that the plasmaacceleration efficiency is dependent upon dimensionless parameter q:q=l ² C ² U ² ₀/2mL ₀,

where l [H/m] is the linear inductance of accelerator electrodes;

C [F] is the capacity of an external discharge circuit;

U₀ [V] is the initial voltage of an external discharge circuit;

m [kg] is the weight of a plasma coagulate;

L₀ [H] is the initial inductance of an external discharge circuit.

The physical meaning of the parameter q lies in defining the ratio of atypical value of a magnetic pressure force to a typical value of anaccelerated plasma coagulate inertia force. It has been established thatan increase in the parameter q results in that a discharge approaches anonperiodic shape with rising of plasma acceleration efficiency.

One of the known features of a pulsed plasma accelerator is that weightm of accelerated plasma is commonly proportional to the power W_(o)applied to the discharge:m≈kW₀,

where W₀=CU² ₀/2;

k=10⁻⁸-10⁻⁹ kg/J is a proportionality factor.

When the dependence for W₀ is introduced in the previous ratio, thedependence for the parameter q assumes the form of:q=1² C ² U ² ₀/2k(CU ² ₀/2)L ₀=(l ² /k)(C/L ₀).

So, with the assigned configuration and sizes of an accelerating channelof a pulsed plasma accelerator, the efficiency of plasma acceleration ischaracterized by the ratio of C/L₀.

The specific technical solutions aimed at increasing the efficiency ofplasma acceleration by means of a pulsed plasma accelerator andassociated with the realization of theoretical reasoning of q of aboutC/L_(o) are not yet developed.

As an example, it is renowned a pulsed plasma accelerator designed foruse as an electric propulsion of a system for controlling the positionof a geostationary earth orbit satellite of a global communicationsystem (A. I. Rudikov, N. N. Antropov, G. A. Popov. “Pulsed PlasmaThruster of Erosion Type for a Geostationary Artificial EarthSatellite”, 44th Congress of the International Astronautical Federation,IAF-93-S.5.487, Graz, Austria: IAF, Oct. 16-22, 1993). Propulsive pulsesgenerated by such a propulsion unit must neutralize the effects of outerfactors upon a spacecraft in a geostationary orbit.

Each pulsed plasma accelerator incorporated in a propulsion unit of theprior art comprises electrodes (a cathode and an anode), one of theelectrodes being made in the form of a copper rod and the other of theelectrodes being made in the form of a plate, a solid dielectric workingsubstance ablating under the action of an electric discharge, a systemfor supplying of a working substance into a rail-type discharge channel,and a discharge-initiating system. Power is supplied to acceleratorelectrodes via current supplies from an outer energy accumulator of 36μF capacitance at the maximal voltage of about 3 kV.

Such an accelerator operates at a gas pressure less than 10-4 torr in anaccelerating channel. The energy released with each pulse is about 160 Jat the current pulse amplitude of 35 kA. The disadvantage of the givenpropulsion unit is low propulsive efficiency, which is less than 10%,owing to an oscillating nature of a discharge current variation duringeach pulse time.

In another pulsed plasma accelerator of the prior art (P. J. Turchi“Directions for Improving PPT Performance”, 25th International ElectricPropulsion Conference, IEPC 97-038, USA, Cleveland, Ohio: IEPC, Aug.24-28, 1997), pulsed oscillating discharges were generated in adischarge channel with power being supplied to electrodes from ahigh-current capacitive accumulator. The stored energy of theaccumulator was 20 J at an initiating voltage of 2 kV, and theaccumulator capacitance was 10 μF. The inductance of an externalelectric circuit was 400 nH. However, despite the attempts of increasingthe pulse time and creating a quasi-continuous discharge current at eachpulse, the total propulsive efficiency of the propulsive unit did notreach 10%. The obtained propulsive efficiency does not allow such plasmaaccelerators to be employed in commercial spacecrafts.

With regard to the paper discussed, it should be mentioned that a properconclusion was drawn on the need for coordination of impedances forinternal and external circuits in a pulsed plasma accelerator. However,quite complicated and low-effective solutions are offered for handlingthe given problem, said solutions including the incorporation ofadditional components in the electric circuit. The mentioned components,such as capacitors, inductance coils and commutators, allow the internaland external circuits to be coordinated and a quasi-nonperiodicdischarge in a pulsed plasma accelerator to be obtained, though thepositive effect is substantially reduced by power losses associated withsuch components.

Apart from the above-mentioned, there exists other viewpoint concerningwith an increase in the efficiency of a pulsed plasma accelerator. As anexample, a pulsed plasma accelerator (propulsion) is known whichcomprises an accelerating channel defined by two electrodes, aninsulator adapted for separating these electrodes and serving as aworking substance, a discharge-initiating system, and an energyaccumulator based on high-current capacitors and connected to theelectrodes by means of a current supply. The given propulsion usesteflon as a working substance (Gregory G. Spanjers et al. “Investigationof Propellant Inefficiencies in a Pulsed Plasma Thruster”, AiAA-96-2723,32nd JPC, Lake Buena Vista, Fla., USA: AIAA/ASME/SAE/ASEE, Jul. 1-3,1996). During operation of the propulsion, the influence of electricdischarge energy upon the efficiency of use of a working substance wasinvestigated. However, despite the resultant increase in a propulsivepulse and propulsion value, the total propulsive efficiency of theplasma accelerator at the discharge energy of about 40 J varied from 7%to 8%. The relatively low propulsive efficiency was due to theoscillating nature of the discharge current variation during each pulse.

The conclusion was drawn in the discussed paper that in order toincrease an efficiency of a pulsed plasma accelerator, the first onehalf-period time of a discharge current must be reduced and itsamplitude must be increased. The above conclusion was supported byreliable experimental results, however it did not take into accountnonlinearity of processes occurred in the input electric circuit of thepulsed plasma accelerator and caused by plasma.

In order to increase propulsive characteristics of pulsed plasmaaccelerators (propulsions), accelerators were designed for high level ofelectric discharge energy (W. J. Guman and D. J. Palumbo “Pulsed PlasmaPropulsion System for North-South Stationkeeping”, AIAA-76-999, AIAAInternational Propulsion Conference, Key Biscayne, Fla., USA: AIAA, Nov.14-17, 1976). A known pulsed accelerator (propulsion) includes twoelectrodes defining an accelerating channel, dielectric bars made fromteflon and arranged between the electrodes, a ceramic end insulator, anda capacitive accumulator. The capacitance of the accumulator was ratedfor the generation of an electric discharge of about 750 J in theaccelerating channel.

The discharge generated in the discharge channel of the present plasmaaccelerator is of oscillating type. The maximal total propulsiveefficiency of the propulsion at the discharge voltage of 2.5 kW was25.6%. However, with the indicated level of discharge energy thepropulsive efficiency of the plasma propulsion may not be acceptedsufficient since the efficiency of competitive plasma (magnetic plasma)propulsions, such as steady-state plasma propulsions, is up to 45% atthis energy level.

It is known a pulsed plasma accelerator (propulsion) comprising two flatcopper electrodes, two dielectric bars manufactured from an ablatingmaterial and arranged between the said electrodes, adischarge-initiating device, and an energy accumulator (N. Antropov etal. “Parameters of Plasmoids injected by PPT”, AIAA 97-2921, 33rdAIAA/ASME/SAE/ASEE Joint Propulsion Conference, Seattle, Wash., USA:AIAA/ASME/SAE/ASEE, Jul. 6-9, 1997). An accelerating channel of theplasma accelerator is defined by surfaces of the electrodes and sidesurfaces of the dielectric bars. The energy accumulator includes fivehigh-current capacitors with the total stored energy of 80-100 J. Theoperating voltage of the capacitor battery is 2.5-2.8 kV. The inductanceof an external electric circuit connected to the electrodes ofaccelerator was 20 nH. The efficiency of plasma accelerator did notexceed 13% with the energy of electric discharge of 100 J.

The closest analog of the claimed invention is an erosion (ablation)plasma propulsion (accelerator) disclosed in Pat. No RU 2143586 C1(IPC-6 F03H1/00, H05H1/54, published 27 Dec. 1999). The known analogincludes electrodes (a cathode and an anode), which are connected via anohmic and inductance load to a capacitor (energy accumulator) plates, aceramic end insulator, which separates the electrodes from one another,and dielectric bars made from ablating material and arranged between theelectrodes. The energy accumulator is connected to the electrodesthrough thin copper busbars (current supplies). The discharge channelwalls are defined by the surfaces of electrodes and dielectric bars. Theelectrodes of the known plasma accelerator are made in the form ofplates. A discharge-initiating device (igniter) is located in a slotformed in the end insulator.

The dielectric bars used in the known plasma accelerator are movabletoward a discharge channel midline by means of a special moving device(a spring pusher). The dielectric bars are caused to move until abutmentagainst a stop made in the form of a step on the surface of electrode.

Plasma is accelerated in the discharge channel of the plasma acceleratorin the following manner. A narrow high-voltage pulse is supplied from adischarge-initiating unit to the electrodes of the discharge-initiatingdevice. A surface breakdown results in generating of a plasma coagulate,which causes short-circuiting of the electrodes in the slot of the endinsulator where an electric arc discharge is created. During breakdown,electrodes are at a “waiting” potential. A working substance isevaporated from the surfaces of the dielectric bars by radiant dischargeenergy, ionized and accelerated by electromagnetic force and gas dynamicpressure.

During operation of a plasma accelerator-analog, cord-shaped stableplasma is generated at the leading end of the accelerating channel toinhibit deposition of a carbon film in this part of the channel and,accordingly, eliminate non-uniform consumption of the working surface ofdielectric bars. This phenomenon enhances the stable propulsivecharacteristics of the accelerator due to the uniform evaporation of theworking substance.

The electric discharge in the accelerating channel of the plasmaaccelerator is of oscillating nature, with the number of one-halfperiods of pulse discharge current variations being three. As a result,the maximal propulsive efficiency of the plasma accelerator does notexceed 14%.

With the known ablation pulsed plasma accelerator, one of the greatestproblems immediately affecting the efficiency characteristics of theaccelerator are the working substance losses occurring in theaccelerating channel during the plasma acceleration process.

The reason for the working substance losses has to do with space andtime discrepancies of the two processes occurring in the acceleratingchannel of the pulsed plasma accelerator:

-   -   a relatively fast process (t_(pr) of about 1.5-3 μs) of        formation and acceleration of a discharge current region (a        current arc);    -   a relatively slow process of heating the working surfaces of the        working substance bars, ionization of the working substance,        generation of a plasma flow and acceleration thereof (t_(pr) is        about 7-12 μs).

The total oscillatory electric discharge time of the known pulsed plasmaaccelerator-analog is 8-15 μs depending on the sizes of the acceleratingchannel and the features of the discharge circuit. However, as it hadbeen established, an effective electromagnetic process for plasmaacceleration occurred only during the first discharge of the accumulator(the first one-half period of the discharge current), with the time ofthe said discharge making from 1.5 to 3.0 μs depending on the energy andsizes of the accelerator. Furthermore, in the course of the dischargeprocess, only the ablation (evaporation) of the working substance andthermal (gas dynamic) plasma acceleration had occurred.

DISCLOSURE OF THE INVENTION

The invention is aimed at increasing the share of a working substanceeffectively accelerated by the electromagnetic force in an acceleratingchannel of a pulsed plasma accelerator by using the synchronizedprocesses of intensive ablation of dielectric bars and generation of thethree-dimensional electromagnetic force and using said force foracceleration of an ionized working substance. Synchronization of theabove processes is provided by the greatest possible approximation ofimpedances of external and internal electric circuits of a plasmaaccelerator.

Technical results achievable by utilizing the invention are as follows:increased efficiency in the use of a working substance, reduced electricpower losses in an external electric circuit and increased efficiency ofplasma acceleration in a discharge channel of a pulsed plasmaaccelerator (propulsion efficiency of a pulsed plasma accelerator usedas an electric propulsion). The given technical results are correlatedwith one another and on the whole determine the effectiveness of apulsed plasma accelerator and a plasma acceleration process.

The above results are achieved through the use of a pulsed plasmaaccelerator comprising two electrodes, dielectric bars manufactured fromablating material and arranged between the said electrodes, a dischargechannel with an open end part and walls defined by the surfaces ofelectrodes and dielectric bars, an energy accumulator, current suppliesadapted for connecting of the electrodes to energy-storage accumulatorsand defining in conjunction with the electrodes and the accumulator anexternal electric circuit, an insulator arranged between the electrodesat the end part of the discharge channel opposite the open end part, anda discharge-initiating device.

According to the present invention, the plasma accelerator ischaracterized in that parameters of the accelerator external circuit areselected on the basis of the following condition:2≦C/L,

where C is electric capacitance of the external electric circuit, μF;

L is inductance of the external electric circuit, nH, with the value ofinductance being selected on condition of L≦100 nH.

The above conditions for selecting the parameters of the externalelectric circuit (C and L) actually mean that, concentrated in theaccumulator, the electric capacitance of discharge circuit of theaccelerator increases from the level of about 10-30 μF common for apulsed plasma accelerator to the level of about 40-500 μF depending onthe level of discharge energy and the inductance L of the externalelectric circuit of the pulsed plasma accelerator.

Selection of the range of L and C values was inspired by the followingconsiderations.

With an increase in the circuit capacitance concentrated in theaccumulator, the time of the first one-half period of the electricdischarge rises from about 1.5-3 μs to about 7-10 μs, the dischargebeing transformed from a sine glow discharge with characteristic numberof one-half periods of from 4 to 6 into a quasi-nonperiodic discharge,with the result that this influences significantly on the physicalmechanism of the process in the accelerating channel of pulsed plasmaaccelerator.

With the selected conditions for the pulsed plasma accelerator atrelatively low discharge energy of about 20-60 J, a discharge currentpulse with two oscillation one-half periods may be produced, with theenergy of the second discharge of the accumulator being less than 20% ofthe energy of the first discharge.

According to the present view, only 20-40% of the working substanceevaporated from the dielectric wall surface escape from the acceleratingchannel of the pulsed plasma accelerator at speeds of the order of 20-30km/s. It is the part of the working substance that is accelerated by athree-dimensional electromagnetic force (J×B) resulting from theinteraction of the discharge current with the self-magnetic field. Theremaining 60-80% of the working substance escape from the acceleratingchannel of the pulsed plasma accelerator at subthermal and thermalspeeds of about 0.5-5.0 km/s. This is due to the fact that there is notime available for the evaporated working substance to interact with thedischarge current during the current pulse time. As a consequence, theweighted mean rate values of plasma at the accelerating channel outletend with acceptable values of a single propulsive pulse do not normallyexceed 8-12 km/s. This is characteristic for a propulsion with a “fast”current one-half period (≦3 μs). An increase in the current one-halfperiod time results in an increase in the mass of the working substancethat is effectively accelerated by an electromagnetic force, and,accordingly, in an increase in the propulsive efficiency of the plasmaaccelerator.

The weighted mean rate of flow of the working substance escaping fromthe accelerating channel with the time of first one-half period of ˜7-10μs is 15-22 km/s, which is sufficiently close to the speed of a currentarc (discharge current) along electrodes of the pulsed plasmaaccelerator. According to the calculations, such a rate is 25-30 km/sfor the pulsed plasma accelerator under consideration and is the maximumplasma flow rate. It is obviously not 20-40% of the working substancethat are involved in an electromagnetic acceleration process, as itcommonly occurs in case of a “fast” discharge, but about 70% of theworking substance generated in the accelerating channel. The givenphenomenon was supported by the results of experimental investigationswith laboratory models of pulsed plasma accelerators.

With regard to an increase in the efficiency of a pulsed plasmaaccelerator, of importance is a substantial reduction (by 30-40%) in theconsumption of a working substance. Such a reduction occurs with anincreased discharge time. The phenomenon is attributable to thedecreased discharge current amplitude and, as a consequence, thedecreased intensity of energy emission from the current arc zone. Theemission of the current arc is the basic condition for heating andevaporating of the dielectric working substance.

The decreased consumption of the working substance is also attributableto the variations in the discharge current dynamics in the pulsed plasmaaccelerator. Such variations are due to the fact that the zone withhigher density of current channels (the current arc) comes outimmediately to the edges of electrodes, as in the case with analogs ofthe pulsed plasma accelerators. However, contrary to the known analogs,the discharge does not die out in the given zone during recharging of anaccumulator (with following reversal to the leading part of thedischarge channel), but is in a fixed position for 5-6 ms. So, thecurrent density zone is relatively far from the working substance barsfor a relatively prolonged time interval to result in substantiallyreduced evaporation of the bars.

Also, reduction in the losses of energy in an external electric circuitmay play a crucial role in increasing of propulsive efficiency of apulsed plasma accelerator. Reduction of losses occurs primarily in thecapacitive energy accumulator due to the improved coordination ofparameters of the external electric circuit (the energy accumulator,current supplies for supplying of current to the electrodes) and theinternal electric circuit (the current arc-electrodes) of the pulsedplasma accelerator.

According to the previously obtained test data, the characteristicinductance level of the external circuit in the pulsed plasmaaccelerators of the known types is at least 100 nH and the capacitanceis about 10-30 μF. So, the external circuit impedance calculated from anexpression Z_(ext)=2(L/C) ½ is about 200 mOhm (the active electricalresistance of the circuit may be neglected due to its low value ascompared to the reactive electrical resistance).

The internal circuit impedance dependent on the linear inductance l ofthe discharge channel and speed V of the current arc is calculated fromthe dependence: Z_(int)=1·V/2. The internal circuit impedance is in theaverage about an order of magnitude lower than the external circuitimpedance and is about 20 mOhm.

Inadequate coordination of the external and internal electric circuitimpedance results in dissipation of a significant part of dischargeenergy in the external electric circuit, primarily in the energyaccumulator having relatively higher active electrical resistance, whichis due to the development of an oscillation process in the externalelectric circuit. In such a case the current curve is shaped as anattenuating sine. However, as it had been experimentally established,the current arc effectively accelerates plasma only during the firstone-half period of discharge current, when significant energy is appliedto the discharge and electromagnetic force (J×B) is of substantialvalue.

In the claimed pulsed plasma accelerator, the external electric circuitimpedance Z_(ext) is ˜40 mOhm, which is due to the optimization of theexternal circuit by selecting the parameters C and L in accordance withthe above conditions. The given impedance level is substantially closerto that of the internal electric circuit than in the known analogs. So,with the exploitation of the present invention, the parameters of theexternal and internal electric circuits are maximally coordinatedwithout complicating of the power supply system and additional powerlosses.

Based on test data, the efficiency of plasma acceleration process in thepulsed plasma accelerator, according to the embodiment of the presentinvention, was in the range from 12% to 35%, with the consumed energyvarying from 20 to 150 J.

The indicated efficiency of the pulsed plasma accelerator is in theaverage about twice as large as the propulsive efficiency of the knownaccelerators-analogs for the range of the consumed energy underdiscussion. Furthermore, the approximation dependences have shown thatwith the values of up to 500 J, the propulsive efficiency of the claimedpulsed plasma accelerator is also about twice as large as that of theprototype accelerator.

With an increase in the consumed energy, the overranging of saidefficiency tends to decrease so that with the power of 0.9-1.0 kJ theefficiency values of the claimed pulsed plasma accelerator and that ofthe prototype accelerator are much the same. This is due to aninevitable approximation of critical parameters (L and C) of theirelectric circuits and also due to an increase in the discharge voltagewith the rise of the consumed energy.

On the basis of the above grounds, it is advisable that an additionallimitation of 2≦C/L≦5 be imposed on characteristics of the externalelectric circuit of the pulsed plasma accelerator. The given conditionoutlines an additional limitation on the level of energy accumulated inthe accumulator. The most significant overranging in the efficiency ofplasma acceleration process as compared to that of the prototypeaccelerator is provided when the above condition is observed.

The inductance of the external electric circuit of the claimed pulsedplasma accelerator is selected in the range of L=20-100 nH. Theabove-sited condition is also aimed at keeping a substantial overrangingin the efficiency of plasma acceleration process with the exploitationof the claimed pulsed plasma accelerator as compared to the prototypeplasma accelerator.

It has been found on the basis of investigation results that an increasein the external electric circuit inductance by more than 100 nH leads tothe gradual approximation of parameters of the claimed pulsed plasmaaccelerator and the prototype accelerator. It should be taken intoconsideration that the minimal energy consumption must be appropriate tothe minimal circuit inductance. The value of inductance L below 20 nH ina workable electric circuit of a pulsed plasma accelerator ispractically unrealizable with acceptable conditions for the given typeof apparatuses.

In order to simplify the construction of the pulsed plasma accelerator,electrodes may be made in the form of plates.

The length of electrodes is preferably surpassing the section size ofdielectric bars in the direction of plasma acceleration to provide foradditional increase in the efficiency of plasma acceleration process.

The dielectric bars may be made movable toward a discharge channelmidline. The accelerator is equipped with retainers for fixing thedielectric bars in an appropriate position and with a device for movingthe latter. The present embodiment of the accelerator allows theoperating time of the pulsed plasma accelerator to be substantiallyincreased without replacement of dielectric bars.

The insulator arranged between the electrodes may be equipped with aslot facing an accelerating channel. Such an embodiment of the pulsedplasma accelerator improves the uniformity of evaporation of workingsubstance from dielectric bar surface with time.

In order to eliminate deposition of carbon of the working substance(teflon or fluoroplastic) on the surface of dielectric bars of thepreferred embodiment of the pulsed plasma accelerator, the insulatorarranged between the electrodes is equipped with protrusions facing thedielectric bars. In this case, the dielectric bars are provided withslots configured in conformance with the protrusions of the insulator.

Each of the dielectric bars may be equipped with at least onelongitudinal protrusion facing the respective electrode. Such anembodiment of dielectric bars and electrodes allows ineffective lossesof the working substance to be reduced.

It is desirable that the surfaces of the dielectric bars facing thedischarge channel be made beveled with respect to the midline of thedischarge channel.

In such a case, the distance bmin between the opposite surfaces of thedielectric bars on the side of an end insulator and the distance bmaxbetween the opposite surfaces of the dielectric bars on the side of theopen end of the discharge channel must meet the condition:b_(max)/b_(min)≧1.2. The present embodiment of the pulsed plasmaaccelerator allows the plasma acceleration process to be stabilized withtime.

In order to improve the efficiency of plasma acceleration process, inanother preferred embodiment of the pulsed plasma accelerator the partsof electrodes arranged behind the dielectric bars in the direction ofplasma acceleration may be positioned at an angle α with respect to thedischarge channel midline, the angle α being selected on the conditionthat 10°≦α≦40°.

For increasing the efficiency of plasma acceleration process in theaccelerating channel of the pulsed plasma accelerator, the parts ofelectrodes arranged behind the dielectric bars in the direction ofplasma acceleration may be made continuously narrowing in the directionof plasma acceleration. The maximal width d_(max) and the minimal widthd_(min) of the electrodes are selected in accordance with the condition:d_(max)/d_(min)≧2.

It is also advisable that the length and width of one of the electrodesserving as an anode exceed the length and width of the other electrodeserving as a cathode. An increased length of the anode allows theuniformity of current density to be achieved at the surface ofelectrodes in the pulsed plasma accelerator, particularly, on their endparts adjacent to the discharge channel edge. The result is that withminimal sizes and weight of the electrodes, the performance reliabilityof the pulsed plasma accelerator is improved. The given result is gainedby eliminating the operating modes involving an increased local currentdensity, at which breakdown of the anode may occur.

The possibility of achieving the above result is attributable to thefollowing physical processes supported by the test data.

In the part of the discharge channel of the accelerator defined by thedielectric bars, the concentration of plasma at the anode is twice aslarge as the concentration of plasma at the cathode. The dielectric barsare consequently consumed more intensively near the surface of anode ascompared to the consumption of dielectric bars near the surface ofcathode. A discharge spot occupies the larger area on the anode than onthe cathode. In case the electrodes are of equal size (area), inparticular of width, the major part of the discharge current isconcentrated at the longitudinal edges of the anode. As a result of thisphenomenon, the edges of the anode are subjected to enhanced erosionwith subsequent destruction thereof. An increased width of anode ascompared to that of cathode substantially reduces the probability ofdevelopment of the given adverse phenomenon owing to the increaseduniformity of current density over the surfaces of electrodes.

The speed of advancement of the discharge spot along the surface ofanode behind the edges of dielectric bars is greater than the speed ofadvancement of the discharge spot over the surface of cathode by 30% dueto the Hall effect which shows itself in turning (inclining) of thecurrent arc relative to the surface of electrodes in the direction ofplasma acceleration. An increase in the length of anode (as compared tothat of cathode) eliminates holding of the discharge spot on its outsideedge and, accordingly, reduces the probability of destruction of theelectrode thanks to the increased uniformity of the discharge currentdensity at the surface of electrodes.

The above technical results are also achieved by effectuating a methodfor plasma acceleration, which includes the steps of igniting adischarge in the discharge channel of the pulsed plasma accelerator bymeans of a discharge-initiating device and pulsed supplying of adischarge voltage from the energy accumulator through the externalelectric circuit to the plasma accelerator electrodes between which arearranged dielectric bars of ablating material. According to the presentinvention, quasi-nonperiodic pulsed discharges are ignited in thedischarge channel and maintained at the discharge voltage U of at least1000 V and the external electric circuit characteristics satisfying thecondition: 2≦C/L,

where C is the capacitance of the external electric circuit, μF,

L is the inductance of the external electric circuit, nH, with the valueof capacitance being selected on the condition: L≦100 nH.

In accomplishment of the claimed plasma acceleration method, theimpedance of the external electric circuit maximally approaches theimpedance of an internal electric circuit owing to the selection of theexternal electric circuit parameters (C and L) in accordance with theabove condition. Such coordination of parameters of the electriccircuits is reached without employment of additional apparatuses and, asa consequence, without additional energy losses. The result is that theefficiency of the plasma acceleration process with the consumed energyin the range of 20 to 150 J is about twice as large as the propulsiveefficiency of the known pulsed plasma accelerators. In accomplishment ofthe claimed method, the plasma acceleration process goes on in a stablemanner and is characterized by a highly effective consumption of theworking substance.

The preferred embodiment of the method is provided when thequasi-nonperiodic discharges are ignited and maintained with theexternal electric circuit characteristics selected on the basis of anadditional (limiting) condition: 2≦C/L≦5. The given condition offers thelimitation of the discharge energy level at which a substantialoverranging of plasma acceleration efficiency and working substanceconsumption is shown as compared to the known plasma accelerationmethods.

The approximation dependences evidence that up to the discharge energyvalue of about 500 J, the propulsive efficiency of the plasmaacceleration method exceeds the efficiency of the known methods-analogsby as much as 2-2.5 times. With the discharge energy above 1000 J,however, the efficiencies of the plasma acceleration processes of theclaimed method and that of the known methods-analogues approach close toone another.

It had been also established by investigations that the effect ofsubstantial increase in the efficiency of plasma acceleration processshowed itself at a voltage of no more than 2,000 V. With the indicatedvoltage limitations, the maximal discharge energy is about 1 000 J.

In terms of the set dependences, it is advisable that quasi-nonperiodicpulsed discharges be generated and maintained with the discharge voltageU in the range of 1 000-2 000 V.

It is also desirable that the inductance L of the external electriccircuit be selected in the range of L=20-100 nH. The above additionallimitation is also targeted at keeping the significant overranging ofthe efficiency of plasma acceleration process when realizing the claimedmethod as compared to a prototype method. It had been revealed byexperimental investigations that an increase in the inductance of theexternal electric circuit of more than 100 nH led to a gradualapproximation of parameters of the claimed method and the known one.

In order to simplify the plasma accelerating apparatus, plate-shapedelectrodes were used.

The length of electrodes preferably exceeds the section size ofdielectric bars in the direction of plasma acceleration. The givenembodiment of the means for realizing the method allows the efficiencyof plasma acceleration process to be further increased.

It is advisable that during plasma acceleration process the dielectricbars be moved toward the discharge channel midline until the bars are infixed position with respect to the surfaces of electrodes. The givenembodiment of the means for realizing the method allows a continuousplasma acceleration process to be provided without replacement of thedielectric bars.

It is advisable that plasma acceleration be performed in a dischargechannel, wherein the surfaces of dielectric bars be made beveled withrespect to the discharge channel midline. The distance b_(min) betweenthe opposite surfaces of the dielectric bars on the side of theinsulator and the distance b_(max) between the opposite surfaces of thedielectric bars on the side of an open end of the discharge channel mustsatisfy the condition: b_(max)/b_(min)≧1.2.

The given embodiment of the apparatus allows the plasma accelerationprocess to be stabilized with time. It was experimentally establishedthat during operation of the claimed pulsed plasma accelerator, themaximal consumption of the working substance (dielectric bars) occurrednot in the mid portion of the discharge channel, as it is normally withthe known analogs of a pulsed plasma accelerator, but adjacent to theoutlet section of the discharge channel. The process results in agradual “turning around” of the working surfaces of the dielectric bars.The process is sufficiently prolonged and it takes discharges on theorder of 105 of the energy accumulator. Characteristics of the pulsedplasma accelerator vary (toward an increase) during the above process.The above version of the embodiment of dielectric bars is aimed atreducing the time of running-in of the channel of the pulsed plasmaaccelerator and at stabilizing the characteristics of plasmaacceleration working process, beginning with the first starting of theaccelerator.

Plasma is preferably accelerated in the discharge channel, wherein theparts of electrodes arranged behind dielectric bars in the direction ofplasma acceleration are positioned at an angle α with respect to thedischarge channel midline. The angle α is selected on the condition:10°≦α≦40°. With the above conditions, the efficiency of plasmaacceleration process is further improved.

It is also advisable that the plasma acceleration process be provided inthe discharge channel, wherein the parts of electrodes arranged behindthe dielectric bars in the direction of plasma acceleration be madecontinuously narrowing in the direction of plasma acceleration. Themaximal width d_(max) and minimal width d_(min) of the electrodes areselected in accordance with the condition: d_(max)/d_(min)≧2. In thiscase the linear inductance of the discharge channel is increased toproduce a beneficial effect on the coordination of the external andinternal electric circuit parameters. As is evident from theexperiments, the efficiency of plasma acceleration process is furtherincreased by 10-12% with the use of continuously narrowing electrodes ascompared to rectangular electrodes.

It is advisable that plasma acceleration be provided in a dischargechannel defined by an insulator equipped with a slot arranged on thedischarge channel side. Such an embodiment of the pulsed plasmaaccelerator used as a means for realization of the plasma accelerationmethod allows the uniformity of evaporation of the working substancefrom the surfaces of dielectric bars to be increased with time and,accordingly, the efficiency of plasma acceleration process to be furtherincreased.

In the preferred embodiment, plasma acceleration is performed in thedischarge channel wherein the length and width of one of the electrodesserving as an anode exceeds those of the other electrode serving as acathode. The given version of the embodiment allows erosion of anodeedges to be minimized and, as a consequence, their destruction to beavoided with minimal sizes and weight of electrodes.

BRIEF DESCRIPTION OF DRAWINGS

The group of inventions is illustrated by describing specific examplesof realization with reference to the drawings appended:

FIG. 1 shows a side view of the pulsed plasma accelerator realized inaccordance with the present invention;

FIG. 2 shows a stepped section in A-A planes of the pulsed plasmaaccelerator illustrated in FIG. 1;

FIG. 3 shows a schematic cross-sectional view of the discharge channelin the embodiment of pulsed plasma accelerator using dielectric barsequipped with slots arranged in the region of contacting with theinsulator which brings apart electrodes;

FIG. 4 shows a schematic cross-sectional view in B-B plane of thedischarge channel of the pulsed plasma accelerator presented in FIG. 3;

FIG. 5 shows a schematic cross-sectional view of dielectric barsequipped with longitudinal protrusions facing the electrodes of thepulsed plasma accelerator;

FIG. 6 shows a schematic cross-sectional view of the acceleratordischarge channel, wherein dielectric bars with longitudinal protrusionsare arranged according to the version of embodiment illustrated in FIG.5;

FIG. 7 is a graphic representation of a dependence of a variation in thedischarge current I measured in kA during time T of a current pulsemeasured in μs for a prototype pulsed plasma accelerator;

FIG. 8 is a graphic representation of a dependence of a variation in thedischarge current I measured in kA during time T of a current pulsemeasured in μs for the pulsed plasma accelerator of the presentinvention;

FIG. 9 is a graphic representation of dependencies of a variation indischarge current I measured in kA during time T of a current pulsemeasured in μs for different C and L parameter ratios of an externalelectric circuit of the pulsed plasma accelerator of the presentinvention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The description which follows is an example of the embodiment related tothe construction of the pulsed plasma accelerator realized according tothe present invention and a method for plasma acceleration realized bymeans of the pulsed plasma accelerator. The pulsed plasma acceleratorpresented in FIGS. 1 to 6 comprises two electrodes 1 made in the form ofplates, with one of the plates serving an anode and the other plateserving a cathode. Two dielectric bars 2 of ablating material arearranged between the electrodes. In the case under discussion, anablating material is fluoroplastic. The length of electrodes 1 exceedsthe section size of dielectric bars 2 in the direction of plasmaacceleration.

The walls of a discharge channel of the pulsed plasma accelerator aredefined by surfaces of electrodes 1 and dielectric bars 2. One end partof the discharge channel is made open, and an end insulator 3 isarranged at the opposite end part of the channel between the electrodes1. Refractory ceramics, such as AL₂O₃, is used as a material for theinsulator 3. The insulator 3 is equipped with a slot facing anacceleration channel.

In the example of embodiment under discussion, the slot of the insulator3 is defined by dielectric plates, which are bonded together in such amanner that the surface of a plate-substrate serves as an end wall ofthe slot in the insulator while the beveled edges of two other platesserve as side walls for this slot.

The accelerator also incorporates a discharge-initiating device 4including two electrodes 5 of copper wire. The electrodes 5 are isolatedfrom one another and from the electrode 1 by an isolating refractoryceramic layer. The device 4 is built into the electrode 1 and the copperwire electrodes 5 of the device 4 are facing inside the cavity of theaccelerator discharge channel.

The parts of electrodes 1 arranged behind the dielectric bars 2 in thedirection of plasma acceleration are positioned at an angle α=15° withrespect to the midline of the discharge channel. The value of angle α isselected according to the condition: 10°≦α≦40°. With the aboveembodiment of the electrodes, the distance between the electrodes in theregion of the discharge channel where the dielectric bars 2 are locatedis 45 mm and at the discharge channel edge—60 mm.

Also, the parts of electrodes 1 positioned rearward of the dielectricbars 2 in the direction of plasma acceleration are made continuouslynarrowing in the said direction. The maximal width d_(max) and theminimal width d_(min) of the electrodes are selected on the condition:d_(max)/d_(min)≧2. In the version of embodiment under discussion theindicated ratio (d_(max)/d_(min)) is 7.

The sizes of one of the electrodes 1 serving as an anode exceed that ofthe other electrode serving as a cathode (see in Gigs 1 and 2). In thegiven version of the embodiment, the sizes of the anode (the length andwidth of the anode) exceed the respective sizes of the cathode by 10 mm.With the indicated conditions, the uniform current spreading (theuniform current density at the surfaces of electrodes) is provided withminimal sizes and weight of the pulsed plasma accelerator.

The surfaces of dielectric bars 2 facing the discharge channel are madebeveled with respect to the midline of the discharge channel. Thedistance b_(min) between the opposite surfaces of the dielectric bars onthe side of the end insulator 3 and the distance b_(max) between theopposite surfaces of the dielectric bars 2 on the side of the dischargechannel open end are selected on the condition: b_(max)/b_(min)≧1.2. Inthe version of the embodiment under discussion b_(max)/b_(min)=2.

The dielectric bars 2 are positioned for moving toward the midline ofthe discharge channel. Spring pushers 6 are used as means for moving thedielectric bars 2. The working surfaces of the dielectric bars 2 areheld in the proper position by means of a special retainer 7 made in theform of a protrusion on the surface of electrode 1 serving as a cathode.

For orienting the dielectric bars 2 along the path of movement andfacilitating the uniform ablation of dielectric, recesses 8 may beexecuted on the side surface of bars 2 (see FIGS. 3 and 4). In thiscase, the insulator 3 arranged between the electrodes 1 is equipped withcorrespondingly shaped protrusions 9 facing the dielectric bars 2.

In the version of embodiment shown in FIGS. 5 and 6, each of thedielectric bars 2 is equipped with longitudinal protrusions 10 facingthe electrodes 1. Arrows in FIG. 6 show the direction of advancement ofthe dielectric bars 2 during operation of the pulsed plasma accelerator.

In the version of embodiment under consideration, one longitudinalprotrusion 10 is formed at one side of each dielectric bar 2 facing theelectrode 1 while two protrusions 10 are formed at the opposite side.The given embodiment provides, on the one hand, a stable position forthe dielectric bar 2 and, on the other hand, a minimal surface ofcontacting with the electrode 1 to reduce ineffective consumption of theworking substance.

The plasma accelerator incorporates a capacitive energy accumulator 11including four capacitors 12, two of which being shown in FIG. 1. Theenergy accumulator is structurally connected to the insulator 3 and,accordingly, to the electrodes 1 by means of holding members 13 formedas socket connectors.

The plasma accelerator also includes current supplies 14 and 15manufactured from sheet copper of at least 0.3 mm thick. One end part ofthe current supplies 14 and 15 is connected to electric leads 16 of thecapacitors 12 and the other end part is connected to the relatedelectrode-one of electrodes 1 of the plasma accelerator. Leads 16 of thecapacitors are connected to the current supplies 14 and 15 by means ofthreaded connectors. In order to improve the electric contact, thethreaded connectors are welded.

The current supplies 14 and 15 define in conjunction with the electrodes1 and the energy accumulator 11 the external electric circuit of theplasma accelerator. For reducing the inductance L of the externalelectric circuit, the current supplies are arranged with a minimal gapthere between. The required electric strength in the gap between thecurrent supplies 14 and 15 is provided by locating in the above gap of a0.5 mm thick dielectric fluoroplastic layer (film) 17. The givenembodiment of a connecting unit for connecting the energy accumulator 11with the electrodes 1 is conditioned by need for a minimal value ofinductance L of the external electric circuit (L≦100 nH).

Power is supplied to the electrodes 5 of the discharge-initiating deviceby a power supply unit 18 of the electric discharge-initiating device 4.

The characteristics of the external electric circuit of plasmaaccelerator are selected with the provision that the efficiency of thegiven pulsed plasma accelerator is substantially greater than that ofthe prototype apparatus:2≦C/L,

where C is the electric capacitance of the external electric circuit,μF,

L is the inductance of the external electric circuit, nH, with the valueof inductance being selected on condition: L≦100 nH.

It should be mentioned that the capacitance of the external electriccircuit is concentrated in the immediate region of the capacitors 12 ofthe energy accumulator 11.

Parameters of the external electric circuit providing maximal efficiencyof the plasma acceleration process in the discharge channel of theplasma accelerator are selected with the following additionalconditions:2≦C/L≦5 and L=20-100 nH

The optimal values of the external electric circuit inductance andcapacitance for the embodiment of the plasma accelerator underconsideration are as follows:

L is about 50 nH; C is about 150 μF.

Operation of the plasma accelerator and, consequently, plasmaacceleration method are performed in the following manner.

Upon starting of the pulsed plasma accelerator, an arc discharge isignited in the accelerator discharge channel. A narrow high-voltagepulse of about 1 μs is generated in the power supply unit 18 of theelectric discharge-initiating device and applied to electrodes 5 of thedischarge-initiating device 4. As a result of a high-voltage electricbreakdown over the surface of dielectric, a conducting plasma coagulateis created to short-circuit the electrodes 1 during movement of thecoagulate in the discharge channel.

Upon ignition of the initiating discharge, an electric breakdown occursin a main electrode-to-electrode gap between the electrodes 1, to whichvoltage had been preliminarily applied from the capacitors 12 of theenergy accumulator 11 through the current supplies 14 and 15. Thecurrent supplies 14 and 15 are electrically isolated by means offluoroplastic layer 17 located between the current supplies.

The magnitude of discharge voltage U is selected in the range of from 1000 V to 2 000 V. Voltage pulses are delivered through the externalelectric circuit defined by the energy accumulator 11 and currentsupplies 14 and 15.

The plasma acceleration method is characterized in thatquasi-nonperiodic pulse discharges are generated and maintained in thedischarge channel of the plasma accelerator at the magnitude ofdischarge voltage U of at least 1 000 V and with characteristics of theaccelerator external electric circuit meeting the condition:2L≦C,

where C is the electric capacitance of the external electric circuit,μF;

L is the inductance of the external electric circuit, nF, with the valueof said inductance being selected on the condition: L≦100 nH.

The required inductance of the external electric circuit is provided inthe workable pulsed plasma accelerator by connecting the electrodes 1immediately to the current supplies 14 and 15, which have well developedsurfaces (large area), provided that the length of current supplies andthe distance between current supplies and electrodes are minimal.

In the example of embodiment under consideration, the most optimalcharacteristics L and C of the external electric circuit were selectedwith regard to the achievement of a maximal plasma acceleratingefficiency in accordance with the following limiting condition: 2≦C/L≦5,with the value of inductance L of the external electric circuit beingselected in the range of 20-100 nH.

With the above conditions observed, the best coordination of theexternal and internal electric circuit parameters was stated to causethe achievement of a technical result, which was generally expressed byan increase in plasma acceleration efficiency and reduction ofineffective losses of the working substance and power.

Under the action of emission and convection from the region of electricdischarge, the working substance evaporates (ablates) from the workingsurfaces of dielectric bars 2. The working substance is partly ionizedin the discharge channel of the plasma accelerator with followingacceleration of the resultant plasma coagulate by the electromagneticand gas dynamic forces. Plasma flowing from the discharge channel of theplasma accelerator creates a reactive propulsion.

The embodiment of the end ceramic insulator 3 equipped with a slot onthe side of the discharge channel allows an optimal plasma flow to beprovided at the initial discharge stage, deposition of carbon on thedielectric bars to be avoided and the operating life of plasmaaccelerator to be eventually increased.

To make the most use of the electromagnetic effect during accelerationin the discharge channel of plasma coagulate serving as a current arcbetween the electrodes 1, the electrodes with the length exceeding thesection size of dielectric bars 2 in the direction of plasmaacceleration are used, the said electrodes being made in the form ofplates.

The motion speed of a discharge spot over the surface of one of theelectrodes 1 serving as an anode exceeds by about 30% the motion speedof a discharge spot over the surface of other electrode serving as acathode. At the same time, plasma concentration in the vicinity of thedielectric bars near the surface of the electrode serving as an anode isabout twice as great as that near the surface of the electrode servingas a cathode. The employment of electrodes 1, with the sizes (width andlength) of one of the electrodes serving an anode differing from thoseof the other electrode serving as a cathode by 10 mm, allows theuniformity of current density over the surface of electrodes to besignificantly increased. As a consequence of the given embodiment, theperformance reliability of the pulsed plasma accelerator is increasedwith minimal sizes and weight of the electrodes owing to the eliminationof operating modes of the plasma accelerator with the local holding ofthe discharge spot.

As the dielectric bars 2 are consumed in the process of ablation oftheir working surfaces, the bars 2 are automatically moved toward themidline of the discharge channel by means of the spring pushers 6. Thedielectric bars are fixed with respect to the electrodes 1 in a properposition by means of the retainers 7.

With the evaporation of the material of dielectric bars 2, the beveledshape of their surfaces relative to the midline of the discharge channelis kept: the distance b_(min) between the opposite surfaces of thedielectric bars on the side of the insulator and the distance b_(max)between the opposite surfaces of the dielectric bars on the side of theopen end of the discharge channel satisfy the condition:b_(max)/b_(min)≧1.2.

The above embodiment of the dielectric bars 2 allows the plasmaacceleration process to be stabilized in time by preliminary impartingto the discharge channel of the shape close to the optimalconfiguration.

The embodiment of the end ceramic insulator 3 arranged between theelectrodes 1 and equipped with the protrusions 9 (see FIGS. 3 and 4)facing the dielectric bars 2 and the embodiment of the dielectric bars 2equipped with recesses 8 configured to conform with the shape of theprotrusions 9 allow deposition of carbon on the surface of the leadingend of the dielectric bars 2 to be avoided. It is known that carbon as acomponent of a composition of the working substance-fluoroplasticevaporates, accompanied by deposition on the working surfaces of thebars 2 at the initial operating mode of the accelerator. The givenphenomenon hinders the establishment of an optimal mode of consumptionof the working substance owing to the non-uniform ablation of thesurfaces of bars 2.

The embodiment of the dielectric bars using longitudinal protrusions 10(see FIGS. 5 and 6) facing the electrodes 1 allows the main part of therelatively cold bar 2 to be separated from hot electrodes. This resultsin the reduced influence of the so-called “evaporation aftereffect” ofthe dielectric bars 2. The above effect is due to the evaporation offluoroplastic from the surface of the overheated bar during the pulseddischarge intervals. In this case, the efficiency of plasma accelerationprocess is substantially reduced since a significant part of the workingsubstance is accelerated during the voltage pulse intervals only by agas dynamic pressure.

The results of experimental investigations have shown that with theadvent of a gap between the bars 2 and the hot electrodes 1, theconsumption of the working substance may be reduced by 15-25% dependingon the energy applied to a discharge while plasma accelerationefficiency may be respectively increased.

Usage of the electrodes 1, with the part thereof on the side of thedischarge channel outlet end made continuously narrowing in thedirection of plasma acceleration, allows the linear inductance of thedischarge channel to be increased and the plasma acceleration efficiencyto be improved by 10-12% as compared to electrodes rectangular in planowing to the improved coordination of external and internal electriccircuit parameters. It should be pointed out that an increase in theinductance of the internal electric circuit is more effective ascompared to a reduction in the inductance of the external electriccircuit, which is carried out for coordinating the parameters of theinternal and external electric circuits.

An additional increase in the linear inductance of the discharge channeland, accordingly, an increase in the efficiency of plasma accelerationhas been shown with the use of electrodes 1 whose outlet parts arrangedbehind the dielectric bars 2 in the direction of plasma acceleration arepositioned at an angle α with respect to the midline of the channel. Theoptimal value for the angle α is selected on the condition: 10°≦α≦40°.

An increase in the share of the working substance accelerated by theelectromagnetic force with the total reduction in the consumption of theworking substance is provided on the whole in case characteristics ofthe external electric circuit are selected on the basis of thecondition: 2≦C/L,

where C is the electric capacitance of the external electric circuit,μF;

L is the inductance of the external electric circuit, nH, with the valueof inductance being selected on the condition: L≦100 nH, at thedischarge voltage U of at least 1 000 V.

With the above conditions, quasi-nonperiodic pulsed discharges aregenerated and maintained in the discharge channel of the pulsed plasmaaccelerator owing to the approximation of external and internal electriccircuit impedance values. The given result allows the plasmaacceleration efficiency to be substantially increased by moreadvantageous usage of the working substance and reduced ineffectiveenergy losses in the external electric circuit, primarily in the energyaccumulator. Also, the reduced heating of the energy accumulator due tothe decreased energy losses allows the performance parameters andservice life of the accelerator to be increased.

The efficiency of plasma acceleration in the pulsed plasma accelerator(the propulsive efficiency of an accelerator-propulsion) with the use ofthe pulsed plasma accelerator and plasma acceleration method allowingthe above conditions to be realized, at the discharge energy in therange of 20-150 J may be increased up to 12-35% as compared to theefficiency of 6-16% typical for the known analogs of plasma acceleratorsand plasma acceleration methods.

The achievement of the above technical result with the use of theinvention is supported by the obtained experimental data (see FIGS. 7 to9).

Presented in FIGS. 7 and 8 are the curves of variations in the dischargecurrent I (kA) during the current pulse time T (μs) with the energy W of100 J accumulated in the energy accumulator 8, the said curves beingobtained during operation of a prototype pulsed plasma accelerator andthe claimed pulsed plasma accelerator (FIG. 8).

It follows from the represented graphic dependences that in the firstcase (see FIG. 7) the curve of the discharge current I is an attenuatingsinusoid in shape with four one-half periods, the maximal currentamplitude approaching 60 kA and the first one-half period time of about3 μs.

In the second case (see FIG. 8), vibrations of the discharge current Iattenuate during one one-half period of vibration. The analysis of theprocess has shown that after the first discharge of the accumulator,less than 15% of the stored energy remains therein. The amount of energyremaining in the accumulator is not sufficient for providing the secondbreakdown of the discharge gap during the pulsed discharge of theaccumulator. The maximal amplitude of current during the first one-halfperiod is about 43 kA and the time of the first one-half period is about10 μs.

The results of investigations presented in FIG. 9 are oscillograms ofthe discharge current I of the pulsed plasma accelerator according tothe present invention. The given pulsed plasma accelerator was used torealize the claimed plasma acceleration method. The amount of energystored in the energy accumulator was 20 J. Investigations were performedfor various C and L parameter ratios of the external electric circuit ofthe pulsed plasma accelerator. Three versions of external circuits forthe pulsed plasma accelerator were subject to investigations: theelectric circuit included two, three and four capacitors. The curves“2C”, “3C” and “4C” depicted in FIG. 9 correspond to the above versionsof the external electric circuit.

The C and L parameter ratio changed in accordance with the energyaccumulator capacitance value for each of the above versions of theexternal electric circuit.

The C/L parameter ratio for the curve “2C” was 1, for the curve“3C”—2.6, and for the curve “4C”—3.7. The plasma acceleration efficiency(the propulsive efficiency of a pulsed plasma accelerator-propulsion)for three versions of the external electric circuit of the pulsed plasmaaccelerator was 6.0% (the curve “2C”), 9% (the curve “3C”) and 11% (thecurve “4C”), respectively.

It had been established on the basis of investigations that asignificant increase in plasma acceleration efficiency was exhibited incase the general conditions for selecting the external circuitcharacteristics of the pulsed plasma accelerator were as follows: 2≦CL,

where C is the electric capacitance of the external electric circuit,μF,

L is the inductance of the external electric circuit, nH, with the valueof inductance being selected on the condition: L≦100 nH.

Also, characteristics of the pulsed plasma accelerator were investigatedwith different values of energy accumulated in the accumulator. With thestored energy value W=20 J, the maximal plasma acceleration efficiencywas 11%, with W=60 J-20%, with W=100 J—27% and with W=150 J—33%.Variations in characteristics of the pulsed plasma acceleration with thelarger values W were estimated by approximating the dependences resultedfrom the experiments in the range of high values of energy stored in theaccumulator.

The resultant data suggest that the efficiency of the plasmaacceleration process accomplished by means of the claimed pulsed plasmaaccelerator and realized in accordance with the claimed method is twiceas large as the propulsive efficiency of the known analogues with equalvalues of energy stored in the accumulator.

The Table below represents the results of comparative investigations ofpulsed plasma accelerators, i.e., the prototype and the claimed pulsedplasma accelerator used for realizing the claimed plasma accelerationmethod. The nominal capacitance of energy accumulators (capacitorbatteries) of the accelerators under comparison was established at theequal level W=100 J. TABLE Pulse plasma Pulse plasma Basiccharacteristics of pulse plasma accelerator - accelerator acceleratorsprototype claimed Single propulsive pulse, H · s 2.3 · 10⁻³ 2.8 · 10⁻³Consumption of working substance, 1.9 · 10⁻⁷ 1.5 · 10⁻⁷ kg/pulseSpecific impulse, s 1.25 · 10³   1.85 · 10³   Maximal plasmaacceleration efficiency 14 26 (propulsive efficiency of pulse plasmaaccelerator-propulsion), %

It follows from the above experimental data that though the basiccharacteristics of the prototype pulsed plasma accelerator are higherthan those of the majority known analogs, the said characteristics aremuch lower than the respective characteristics of the claimed pulsedplasma accelerator.

The claimed pulsed plasma accelerator and plasma acceleration methodprovide for higher plasma acceleration efficiency owing to theinvolvement of the larger part of the working substance in theelectromagnetic acceleration process, as compared to the knownanalogues, with the result that ineffective consumption of the workingsubstance is eliminated and energy losses in the external electriccircuit are reduced. The achievement of the above technical resultallows the field of application of the pulsed plasma accelerator to besignificantly widened, the performance reliability of the accelerator tobe enhanced under the conditions of strict limitations with regard tothe weight and size characteristics, and operational costs to bereduced.

INDUSTRIAL APPLICABILITY OF THE INVENTION

The pulsed plasma accelerator and plasma acceleration method realized bymeans of the pulsed plasma accelerator may have applications in variousfields of technique. The pulsed plasma accelerator and plasmaacceleration method may be primarily employed in electric propulsionequipment for spacecrafts. In addition to that, the pulsed plasmaaccelerator may be used for performing in outer space of variousexperiments demanding generation of high-speed plasma flows.

Furthermore, the invention may find a wide utility in surface treatmentprocesses, deposition processes, as well as in producing of novelcomposite materials. Another important trend in applying of theinvention is performing land-based experimental investigations andtesting of the latest samples of equipment by simulating the effects ofhigh-speed plasma flows upon the objects under investigation.

The above example of embodiment of the invention is preferable with theunderstanding that it does not cover any other embodiments of theinvention within the scope of the following claims which may be realizedby means of the equipment and methods well known to those skilled in theart.

1-25. (canceled)
 26. A pulsed plasma accelerator comprising twoelectrodes (1), dielectric bars (2) arranged between the electrodes andmade from an ablating material, a discharge channel with an open endpart, with discharge channel walls being defined by the surfaces ofelectrodes (1) and of dielectric bars (2), an energy accumulator (11),current supplies (14,15) for connecting of the electrodes (1) with theenergy accumulator (11), which together with the electrodes (1) and theenergy accumulator (11) define an external electric circuit, aninsulator (3) arranged between the electrodes (1) at the end part of thedischarge channel opposite to the open end part, and adischarge-initiating device (4), characterized in that thecharacteristics of the external electric circuit of the accelerator areselected on condition: 2≦C/L≦5, where C is the electric capacity of theexternal electric circuit, μF, L is the inductance of the externalelectric circuit, nH, with the value thereof meeting the condition:L≦100 nH.
 27. The accelerator of claim 26, wherein the inductance of theexternal electric circuit is selected in the range of L=20-100 nH. 28.The accelerator of claim 26, wherein the electrodes (1) are made in theform of plates.
 29. The accelerator of claim 26, wherein the length ofthe electrodes (1) exceeds the section size of the dielectric bars (2)in the direction of plasma acceleration.
 30. The accelerator of claim26, wherein the dielectric bars are adapted for advancement toward thedischarge channel midline, with the accelerator being equipped with aretainer (7) for retaining the dielectric bars (2) in a proper positionand a device (6) for advancing said dielectric bars.
 31. The acceleratorof claim 26, wherein the insulator (3) arranged between the electrodes(1) is provided with a slot facing an acceleration channel.
 32. Theaccelerator of claim 26, wherein the insulator (3) arranged between theelectrodes (1) is provided with protrusions (9) facing the dielectricbars (2), and the dielectric bars (2) are provided with recesses (8)configured to conform the shape of protrusions (9) of the insulator (3).33. The accelerator of claim 26, wherein each of the dielectric bars (2)is provided with at least one longitudinal protrusion (10) facing theelectrode (1).
 34. The accelerator of claim 26, wherein the surfaces ofthe dielectric bars (2) facing the discharge channel are beveled withrespect to the midline of the discharge channel so that the distanceb_(min) between the opposite surfaces of the dielectric bars (2) on theside of the insulator (3) and the distance b_(max) between the oppositesurfaces of the dielectric bars (2) on the side of the open end of thedischarge channel satisfy the condition: /b_(min)≧1.2.
 35. Theaccelerator of claim 26, wherein the parts of the electrodes (1)arranged behind the dielectric bars (2) in the direction of plasmaacceleration are positioned at an angle α with respect to the dischargechannel midline, with the value of angle α being selected on condition:10°≦α≦40°.
 36. The accelerator of claim 26, wherein the parts of theelectrodes (1) arranged behind the dielectric bars (2) in the directionof plasma acceleration are made continuously narrowing in the saiddirection, with the maximal width d_(max) and minimal width d_(min) ofthe electrodes (1) are selected according to the condition:d_(max)/d_(min)≧2.
 37. The accelerator of claim 26, wherein the lengthand width of one of the electrodes (1) serving as an anode exceeds thelength and width of other electrode (1) serving as a cathode.
 38. Amethod for plasma acceleration including the steps of igniting adischarge in the discharge channel of the plasma accelerator by means ofa discharge-initiating device (4) and pulsed applying of dischargevoltage from an energy accumulator (11) via an external electric circuitto electrodes (1) of the plasma accelerator between which are arrangeddielectric bars (2) made from ablating material, characterized in thatquazi-nonperiodic pulse discharges are ignited and maintained in thedischarge channel at the discharge voltage U of at least 1 000 V and thecharacteristics of the external electric circuit satisfying thecondition: 2≦C/L≦5, where C is the electric capacitance of the externalelectric circuit, μF, and L is the inductance of the external electriccircuit, nH, with the capacitance value satisfying the condition: L≦100nH.
 39. The method of claim 38, wherein the quazi-nonperiodic dischargesare ignited and maintained with the discharge voltage U=1 000-2 000 V.40. The method of claim 38, wherein the inductance L of the externalelectric circuit is selected in the range of L=20-100 nH.
 41. The methodof claim 38, wherein plasma acceleration is provided by means ofelectrodes (1) made in the form of plates.
 42. The method of claim 38,wherein plasma acceleration is provided by means of electrodes (1)having length exceeding the section size of dielectric bars (2) in thedirection of plasma acceleration.
 43. The method of claim 38, wherein inthe process of plasma acceleration, the dielectric bars (2) are movabletoward a midline of the discharge channel until they are fixed withrespect to the surface of the electrodes (1).
 44. The method of claim38, wherein plasma acceleration is provided in the discharge channelwherein the surfaces of the dielectric bars (2) are made beveled withrespect to the discharge channel midline so that the distance b_(min)between the opposite surfaces of the dielectric bars (2) on the side ofthe insulator (3) and the distance b_(max) between the opposite surfacesof the dielectric bars (2) on the side of the open end of the dischargechannel satisfy the condition: b_(max)/b_(min)≧1.2.
 45. The method ofclaim 38, wherein plasma acceleration is provided in the dischargechannel, wherein the parts of electrodes (1) arranged behind thedielectric bars (2) in the direction of plasma acceleration arepositioned at an angle α to the discharge channel midline, with thevalue of angle α being selected on the condition: 10°≦α≦40°.
 46. Themethod of claim 38, wherein plasma acceleration is provided in thedischarge channel, wherein the parts of electrodes (1) arranged behindthe dielectric bars (2) in the direction of plasma acceleration are madecontinuously narrowing in the said direction, with the maximal widthd_(max) and the minimal width d_(min) of the electrodes (1) are selectedon the condition: d_(max)/d_(min)≧2.
 47. The method of claim 38, whereinplasma acceleration is provided in the discharge channel defined by theinsulator (3) wherein a slot is formed on the side of the dischargechannel.
 48. The method of claim 38, wherein plasma acceleration isprovided in the discharge channel wherein the width and length of one ofelectrodes (1) serving as an anode exceeds those of other electrode (1)serving as a cathode.